1. Field of the Invention
The present invention generally relates to personal watercraft, and more particularly relates to propulsion control based on detected attitude of a personal watercraft.
2. Description of the Related Art
Typically, water-jet propulsion personal watercraft have a relatively small body including a hull and a deck covering the hull from above which are joined to each other. An engine is mounted in an inner space of the body. The engine is configured to drive a water jet pump configured to propel the watercraft, which pressurizes and accelerates water sucked through a water passage from a water intake generally provided on a hull bottom surface, and ejects it rearward from an outlet port. As a result, the personal watercraft is propelled.
Since the personal watercraft has a relatively small body as described above, it may have various travel attitudes depending on a reaction force of a water jet ejected from the water jet pump or an operating attitude of a rider. For example, when the rider performs an operation to quickly open a throttle to a great degree to gain a large propulsion force of the watercraft, a front part of the body tends to tilt upward. When the rider operates a steering handle to a great extent to perform a sharp turn, the watercraft body tends to bank in a steering direction.
However, with the front part of the body tilting upward to a great extent, the propulsion force being generated by the water jet pump is not efficiently utilized to accelerate the watercraft in a direction in which the watercraft is traveling, and therefore, a desired acceleration is not achieved. If the watercraft banks to a great extent during the turn, the water intake on the hull bottom surface is exposed above the water surface, and air enters the water jet pump through the water passage. As a result, the propulsion force of the watercraft may decrease.
In the water-jet propulsion personal watercraft, a steering nozzle is disposed behind an impeller of the water jet pump. By pivoting the steering nozzle clockwise or counterclockwise, a water jet ejected from the water jet pump is changed to turn the watercraft. With the throttle in a fully closed position, the water jet ejected from the water jet pump is little, making it difficult to turn the watercraft.
By way of example, Japanese Laid-Open Patent Application Publication No. 2001-191992 discloses a steering assist function to assist in enhancing steering function when the throttle is in a fully closed position and thereby the steering function degrades. More specifically, steering tabs (movable tabs) which are movable and are capable of being submerged in water, are caused to provide different propulsion resistances to the right and to the left to assist in turning the watercraft.
In the above configuration, however, since the steering tabs are typically configured to cooperate with the steering handle, they may provide an undesired turning capability during travel in medium and high speed ranges, if the watercraft is configured to fully perform the steering assist function during low-speed travel.